The biochemical and ultrastructural basis for neurite extension and axoplasmic flow in neuroblastoma cells in tissue culture will be investigated. It appears that both the growth of neurites and the flow of materials within them involves a "primitive" motile system which is dependent; at least in part, on microtubules and microfilaments. The contractile proteins of neuroblastoma cells will be isolated by use of methods designed for the isolation of contractile proteins from other "primitive" systems as well as by new procedures. They will be identified by acrylamide gel electrophoresis and by their interactions with the contractile proteins of muscle by use of ATPase assays, viscometry, and electron microscopy. In addition, the possible interaction of contractile proteins of neuroblastoma and muscle with microtubule protein will be tested. Neuroblastoma cells growing on electron microscope grids will be used for the in situ localization of actin-containing filaments by use of heavy meromyosin "decoration"; myosin-like and other contractile proteins will be visualized in situ by use of antibodies to these proteins and negative staining procedures. The control of neurite extension in vivo will be studied by use of inhibitors of protein synthesis (cycloheximide), microtubule assembly (colchicine) and microfilament function (cytochalasin B) along with the appropriate amino acid incorporation studies to determine the requirements for microtubule and microfilament synthesis and assembly during neurite outgrowth. Neurites of single cells will be amputated by micromanipulation to determine the relationship between the growth and resorption of neurites on the same cell. Studies on exoplasmic flow will be carried out with neuroblastoma cells and with primary cultures of neurons from dorsal root ganglia. In these studies, the sites of synthesis and paths of transport will be determined by light and electron microscope autoradiography of pulse-chased cells. Collaborative studies on the use of neuroblastoma cells for investigation of diseases such as phenylketonuria have been begun and their possible use in investigations of other neurological diseases will be initiated.